1. Field of the Invention
The present invention relates generally to the mutual attachment of aerospace vehicle components such as the attachment of one or more booster rocket motors together or to a core rocket vehicle and, more particularly, to the transfer of a thrust load between such vehicle components while permitting varied stand-off distances therebetween.
2. State of the Art
Aerospace vehicle components, such as rocket motors, are used to transport various payloads into space. Such rocket motors typically burn chemical propellants, either solid or liquid, to provide the thrust required during the vehicle""s ascent through the earth""s atmosphere and into orbit. This thrust is achieved by combustion of the propellants, resulting in the ejection of hot gases through a nozzle to the rear of the vehicle. A large amount of thrust is required to launch an aerospace vehicle, the exact amount of thrust varying from one aerospace vehicle to another depending on a number of factors including the payload of the vehicle. The variation of payload in an aerospace vehicle may require considerable reconfiguration of the thrust design including larger or additional booster rocket motors being attached to the core vehicle. The reconfiguration of thrust-providing components often poses design difficulties, particularly with respect to their relation to each other and to launch pad structures.
For example, referring to FIG. 1A, the aft end of a prior art core rocket vehicle 100 is shown positioned in a launch pad structure 102. If booster rocket motors are attached to the core rocket vehicle 100, either the launch pad structure 102 would require reconfiguration to accommodate the booster rocket motors or the booster rocket motors would have to be attached to locate them outwardly of the launch pad structure 102 to avoid physical interference with the launch pad structure 102. As launch pad structures are extremely expensive to design and manufacture, it is often the case that the addition of booster rocket motors (or a change in the size of existing booster rocket motors) involves significant design considerations regarding the manner of their attachment to the core rocket vehicle 100. Such design considerations include not only structural issues of transferring thrust from the booster rocket motor to the core rocket vehicle 100, but the positional or spatial considerations regarding the arrangement of the booster rocket motors relative to the core rocket vehicle 100, an existing launch pad structure 102, or other structures.
Referring to FIG. 1B, a bottom plan view is shown of the launch pad structure 102 with a the core rocket vehicle 100 positioned thereon. With a structure of this configuration, the booster rocket motor location which would allow the closest lateral attachment of a booster rocket motor to the core rocket vehicle 100 (the lateral distance being referred to as the stand-off distance) may be along the centerline 104 which extends radially from the center of the core rocket vehicle 100 and is oriented perpendicularly to the closest side 106 of the launch pad structure 102. However, it may not always be desirable to mount the booster rockets in this location.
For example, if it was desired to utilize four booster rocket motors, the configuration resulting in the shortest stand-off distance might be that shown in FIG. 2. In this case, booster rocket motors 108 have been shifted to one side or another of the centerline 104. By moving the rocket motors laterally from the centerline 104, the stand-off distance is increased.
However, it should be noted that designing the shortest stand-off distance between a booster rocket motor 108 and the core rocket vehicle 100 entails more than just determining the circumferential position of the booster rocket motor 108 relative to both the core rocket vehicle 100 and the launch pad structure 102. Other considerations must be taken into account as well. For example, with reference to FIG. 3, even though the booster rocket motors 108 have been located such that there is no physical interference with the launch pad structure 102, the exit cones 110 of the booster rocket motors are located such that the launch pad structure 102 may be in the path of hot gases exhausted from the exit cones 110. This exposure may lead to costly damage to the launch pad structure 102 or vehicle failure through interference with core rocket vehicle components. Thus, proper arrangement of the booster rocket motors 108 would include an increased stand-off distance to avoid any damage to the launch pad structure 102.
Increases in stand-off distance induces greater stress within the coupling apparatuses utilized to transfer the thrust from the booster rocket motors 108 to the core rocket vehicle 100. With new designs and technology, thrust levels produced by such booster rocket motors are continually being increased. Current levels of thrust produced by booster rocket motors are often several hundred thousand pounds, while contemplated designs reach upwards of 1,000,000 lbs. of thrust. The combination of larger booster rocket motors having increased thrust with the need to provide increased and varied stand-off distances requires improved coupling apparatuses for coupling the booster rocket motors with the core rocket vehicles and transferring the thrust loads therebetween. Additionally, various alignment requirements for booster rocket motors may require an attachment structure which allows greater flexibility regarding where the attachment structure may be located on the core rocket vehicle or the booster rocket motors.
One type of coupling apparatus commonly used to attach booster rocket motors to core rocket vehicles includes a pair of rods or struts, one end of each rod being attached to the core rocket vehicle and the other end of each rod being attached to the booster rocket motor. While such an arrangement may be sufficient for certain combinations of thrust loads and stand-off distances, this type of coupling apparatus suffers from various drawbacks which are only exacerbated as thrust loads and stand-off distances are increased. For example, rods or struts have typically only been effective in coupling booster rocket motors having small stand-off distances (e.g., 2 to 8 inches). However, as the stand-off distance increases, the stress induced within the rod similarly increases. Likewise, the induced stress increases when the thrust of a booster rocket motor increases. Additionally, such coupling apparatuses are designed to transfer thrust substantially through point loading. These point loads are concentrated at individual attachment locations on the booster rocket motor casing and on the core rocket vehicle. Often, such point loading is undesirable, particularly when exerted on composite structures such as are typically used for the booster rocket motor casings.
In view of the shortcomings in the state of the art, it would be advantageous to provide a coupling apparatus for and method of attaching booster rocket motors to each other or to core rocket vehicles and transferring thrust loads therebetween. The structure and method would desirably allow for high stand-off distances to be utilized while efficiently transferring high thrust loads from the booster rocket motor to the core rocket vehicle. Additionally, it would be desirable to provide such a structure having a relatively high strength-to-weight ratio so as to avoid adding unnecessary weight to the overall structure. It would further be desirable to provide a structure and method of attachment which helps reduce the loading and associated stress placed on the casing of the booster rocket motor.
In accordance with one aspect of the invention, an apparatus is provided for coupling a booster rocket motor to a core rocket vehicle and transferring loads therebetween. The apparatus includes at least one load acceptance structure which is configured for load-distributing attachment with the booster rocket motor. At least one load transfer structure is configured for substantial point load attachment with the core rocket vehicle. A structural member is coupled between the structures, the structural member including at least a portion configured as an I-beam. The I-beam may further be configured to exhibit a varied cross section as it extends between the load transfer and load acceptance structures. For example, the flanges of the I-beam may vary in width and/or thickness or exhibit curved sections. Similarly, the web may vary in height and/or thickness. The apparatus may be formed of aluminum, such as 7075 aluminum, or some other suitable material desirably having a modulus of elasticity which is similar to that of the booster rocket motor casing.
According to another aspect of the invention, another apparatus is provided for coupling a booster rocket motor to a core rocket vehicle. The apparatus includes at least one load transfer structure configured for substantial point load attachment with the core rocket vehicle. At least one load acceptance structure is configured for load-distributing attachment with the booster rocket motor. A structural member is coupled between the load transfer and load acceptance structures and exhibits a varied transverse cross section as it extends between the load transfer and acceptance structures. The structural member may include an I-beam configuration or some other structural shape.
According to another aspect of the invention, a method is provided for coupling a booster rocket motor to a core rocket vehicle for the transfer of thrust therebetween. The method includes providing a booster rocket motor having a portion of its case being configured for substantial load-distributing attachment. One or more saddles are formed on a portion of the booster rocket motor, the saddle(s) being configured for load-distributing attachment. An apparatus for coupling the booster rocket and core rocket vehicle is also provided. The coupling apparatus includes a load acceptance structure configured for load-distributing attachment, and a load transfer structure configured for substantial point load attachment, and a structural member having a variable cross section is provided and coupled between the load acceptance and load transfer structures. The load acceptance structure is coupled to the attachment portion of the booster rocket motor and the load transfer structure is coupled with the attachment portion of the core rocket vehicle. The method may also include configuring the structural member of the coupling apparatus as an I-beam exhibiting a varied cross section along its length.
In accordance with yet another aspect of the invention, a method is provided for forming one or more saddles in a composite casing of a booster rocket motor for attachment of a coupling apparatus and, more particularly, to the aforementioned load acceptance structure of a coupling apparatus. The method includes placing a rubber shear ply adjacent an exterior surface of the composite casing. The shear ply may be formed of natural or synthetic rubber such as nitrile-butadiene rubber (NBR) or ethylene-propylene-diene monomer (EPDM). An attachment structure configured for attachment to the coupling apparatus is formed atop the rubber shear ply and a fiber hoop overwrap, such as graphite or fiberglass, is formed over portions of the attachment structure.